Organic light emitting devices (OLEDs) are a type of device having visual emissions from an organic compound. In general, the basic OLED structure consists of a plurality of fluorescent organic layers sandwiched between a transparent conducting anode and metallic cathode. When an appropriate bias is applied to the device, holes are injected from the anode and electrons from the cathode; some of the recombination events between the holes and electrons result in electroluminescence (EL). OLEDs may be found in low information displays such as mobile phones, MP3 players, and digital cameras.
The organic layers are highly susceptible to water and oxygen, with exposure resulting in reduced efficiency in OLEDs or even complete failure. In order to protect the OLED, barrier materials with low permeability of ambient moisture and oxygen are coated on the surface. Several types of polymeric resins have being evaluated for this application such as epoxy resins, polyacrylonitrile, polyvinyl alcohol and its copolymers, poly(lactide), polyethylene terephthalate, poly(vinylidene dichloride), liquid crystal polymers, silicone polymers, polyethylenes, and others. None of these known polymeric barriers demonstrate outstanding barrier resistance to both oxygen and water at the same time. For example, polyvinyl alcohol is an excellent barrier toward oxygen, but very poor barrier toward water. In contrast, high density polyethylene is excellent barrier toward water but poor barrier toward oxygen. “Multi-layer” barriers, inorganic barriers, and sandwiched aluminum thin films have been developed, however, these are not suitable for use with OLEDs due to their processing complexity, and lack of adhesion or optical transparency.
Melamine vapor deposition processes lead to remarkably reduced oxygen permeation when a single layer of melamine was coated on common polymers such as PET or polypropylene. However, the film demonstrates instability due to high moisture absorption of melamine as single molecules (non-polymeric). The melamine film thus produced has solubility in water of 3.24% that indicates it is highly water absorbing. The high water absorbance renders it useless as a barrier film for OLEDs.